Integrated circuits are often formed on substrates, such as substrates of semiconducting material. Such substrates can hold as few as one or many as thousands of the integrated circuits. As the term is used herein, “integrated circuit” includes devices such as those formed on monolithic semiconducting substrates, such as those formed of group IV materials like silicon or germanium, or group III-V compounds like gallium arsenide, or mixtures of such materials. The term includes all types of devices formed, such as memory and logic, and all designs of such devices, such as MOS and bipolar. The term also comprehends applications such as flat panel displays, solar cells, and charge coupled devices.
Integrated circuits are typically formed in a series of process steps, where materials are first added to the substrate in layers, then patterned, and finally etched or otherwise altered before another layer is added. Typically it is extremely difficult to go back and fix a layer that has been improperly formed, after another layer has been formed on top of the malformed layer. For this and other reasons, the substrates are usually given frequent and thorough inspections, such as optical inspections.
A substrate is typically inspected by removing the substrate from the cassette in which it and other substrates are held, and moving the substrate into an inspection system. This substrate handling is usually performed by a robot arm that has been fitted with a head that can engage the substrate. The inspection system typically includes a motorized stage that moves the substrate around underneath the inspection optics. The inspection optics remain in one place, because they tend to include large glass lenses that—because of their weight, size, and delicate nature—cannot be moved as easily as the substrate. Once the inspection is complete, the robot arm removes the substrate from the stage and places it back into the cassette, from which another substrate is removed, and the inspection process is repeated.
Unfortunately, the robot arms required to move the substrates tend to be rather expensive. Further, moving the substrates around in this manner tends to require an appreciable amount of time.
What is needed, therefore, is a system that overcomes problems such as those described above, at least in part.